This invention relates to a novel control circuit for controlling the output power to a load such as a lamp or motor and more specifically relates to a novel phase control circuit in which the input signal is itself a phase controlled signal and in which the power control circuit is positively disconnected from the load circuit in response to the removal of an input signal from the input of the power control circuit.
The invention also relates to a novel interface circuit in which the input signal is a phase controlled signal and the outputs are (1) a variable frequency pulse width modulated,variable voltage or other variable signal and (2) a switched hot output, where the outputs are used to control a high frequency dimming ballast or other power control module, with power being disconnected from the fluorescent dimming ballast via the switched hot output in response to the removal of an input signal from the input of the interface circuit.
Phase control circuits are well known and are commonly used to vary the electrical power applied to a load. For example, phase control circuits are commonly used to control the speed of a motor or the light output of a lighting load. Phase control circuits commonly employ a thyristor such as a silicon controlled rectifier or triac as the switching device. Gate turn off devices, bipolar and MOSFET transistors can also be used. Such devices are hereinafter termed "controllably conductive devices." The gate or control circuit of these devices is constructed with electrical components and operates to cause the controllably conductive device to fire or become conductive at some adjustable time after each zero crossing of the applied power, usually derived from an a-c source. Consequently, voltage is applied to the load in series with the controllably conductive device after a time delay from each zero crossing. The power applied to the load is reduced by an amount related to this phase delay. By varying the time at which voltage is applied to the load, following a zero voltage crossing, one controls the brightness of lights or the speed of a motor, or the like.
Phase control circuits commonly employ an adjustable time delay input circuit, consisting of a resistor and capacitor. The time delay input circuit is then commonly connected to a suitable breakover device such as a diac which becomes conductive when the voltage across the capacitor in the time delay input RC circuit reaches a given value. Upon breakover of the diac, at a controlled time delay after the zero voltage crossing of the input voltage to the time delay circuit, a current is injected into the control lead of the controllably conductive device causing it to become conductive. By making the resistor in the input RC circuit adjustable, one can adjust the time (or phase angle) following a zero crossing of the input voltage that a firing signal is produced to cause the controllably conductive device to become conductive.
It is also common in phase control circuits, particularly those associated with incandescent or fluorescent light dimming, to apply numerous adjustments on the phase angle at which the controllably conductive device is fired in any half cycle. This may be done to compensate for changes in line voltage so that such changes do not affect the output of the circuit; to adjust the "high end trim" (maximum light output) and/or "low end trim" (minimum light output) of the dimmer; to turn on the dimmer (or a motor) with "soft start" in which a dimmer is progressively turned on to a given light intensity by gradually decreasing the phase angle from a maximum value over a given period of time or number of half cycles; or to provide "fade control" so that the light intensity changes at some particular rate when the dimmer control is changed from one value to another, thereby to avoid otherwise annoying rapid changes in light level.
When a large number of dimmers are provided for a dimming system, such as that of the type shown in U.S. Pat. No. 4,575,660, each dimmer of the system may have a full set of signal treating or compensating components. This increases the volume required for the dimmer and further increases the cost of the system. There are also many systems in which a large number of dimmers are to be operated identically but each still requires its full set of adjustment members and controls. Consequently, it is difficult to assemble such dimmers in a small volume and they usually must be assembled in an electrical cabinet which is remote from the respective control members which are usually located conveniently in a wall box mounting. Thus, where high power dimmers, for example dimmers rated at 2,400 or 3,600 watts, are required for a lighting system, it is usually necessary to separate the control devices and the controllably conductive device since the controllably conductive device must be mounted on a relatively large heat sink. Thus, the entire assembly cannot be conveniently located in a wall box along with the manual controls, but must be remotely mounted. By contrast, the entire contents of dimmers rated at up to 2,000 watts can be mounted within a single back box which can in turn be mounted within a suitable wall box.
It is known to have a positive disconnect switch means in series with a voltage control device such as a dimmer where the disconnect is positively open when the dimmer control is operated to a position at which the lights are off or dimmed to a minimum value. The positive disconnect prevents the hazard of working on a load circuit in the mistaken belief that lights dimmed to a minimum are in fact positively disconnected from the power source. Such disconnects commonly are operated when a dimmer control reaches one end of its travel or when a separate toggle is operated. Thus, some positive action is requied of the person operating the dimmer control element, whether a toggle handle or slide handle or the like, in order to obtain the opening of the main disconnect switch. If this is not done but the lights are dimmed to a minimum value, one might be misled to think the disconnect is open.